A 77-year old Russian human rights activist was sentenced Wednesday by a Moscow court to 25 days in jail for calling for an unauthorized protest, a ruling that has drawn strong criticism from rights groups.

Charges against Lev Ponomarev, a highly respected rights activist, stemmed from a Facebook post in which he called for a protest in October in support of several teenagers accused of extremism in a case widely described as trumped up.

Ponomarev was briefly detained when he attended October’s rally outside Moscow headquarters of the main domestic security agency...